A heat exchanger is a device used to transfer heat between an object and a fluid, or between several fluids. They are widely used in space heating applications, refrigeration, HVAC systems, and at scale in power stations, chemical and petroleum plants, natural gas processing, and wastewater treatment.
Typical examples of heat exchangers use pipes and tubes to circulate coolants, heating the air that passes over those coils. Another example is the heat sink, a stack or arrangement of plates that draw heat from an electronic or mechanical device and transfer the heat to the surrounding environment.
The most common use for heat exchangers is for HVAC systems, using air-to-air and water-to-air to regulate building temperatures. They are also used for both cooling and heating large scale industrial processes, with larger units tailored to suit a specific process.